| 摘要 |
PROBLEM TO BE SOLVED: To select a correct optical transmission line at all times even when a switching control section is inserted or withdrawn. SOLUTION: In the case of selecting a standby system of optical transmission lines, a switching control signal 100 outputted by a switching control circuit 141 is at a low level and a reset signal of a power reset circuit 142 is at a high level, then switching control signals 101, 102 outputted from NAND gates 143, 144 are respectively at a high level and a low level. Thus, a set terminal S of a latch circuit 114 goes to a high level and a reset terminal R reaches a low level and its output signal 103 goes to a low level. In this state, when the switching control circuit 14 is withdrawn, the switching control signals 101, 102 given to the latch circuit 141 both go to a high level and the set terminal S and the reset terminal R go to a high level, but since the latch circuit 114 adopts a negative logic input, the output signal 103 remains a low level and then the selection of the standby system for the optical transmission lines is maintained. |
